Audiences might think that chamber musicians have a pretty cushy life, sitting around in a small group, performing nice little pieces, usually fairly short — and they don’t even have to contend with a conductor in front, making emphatic motions and vigorous demands on the players! Well, in case there is any doubt, audience members at the finale of the 2011-12 Four Seasons Chamber Music Festival can attest that chamber music performers don’t always have it so easy. Six string players poured themselves into two highly demanding works, almost panting at the end as they left the stage.

Artistic director Ara Gregorian chose two meaty pieces by Schoenberg and Brahms to close this season, leavened only slightly by his own arrangement of Edward Elgar’s delightful Serenade for Strings in E minor, Op. 20. Gregorian played viola and was joined by violinists Soovin Kim of Stony Brook University and Axel Strauss of the San Francisco Conservatory of Music, cellists Ani Aznavoorian of the University of Illinois and Michael Kannen of the Peabody Conservatory, and violist Hsin-Yun Huang of the Juilliard School and Curtis Institute of Music - a formidable lineup, to be sure, and one that created some memorable music.

All three pieces received excellent playing from start to finish, whether the score focused on the sextet as a whole or on smaller ensembles within the sextet. One especially fascinating aspect to the concert was that each composition (with Elgar aided by Gregorian’s arrangement) included sections in which perhaps a trio alone had a prominent role, or perhaps a quartet, even a quintet. The remaining players did not stay out of the musical mix for long, of course, but these parts of the compositions enabled the listener to hear and appreciate what amounted to inner voices of the larger works. Too, a composition for a string sextet provides great flexibility for that kind of scoring — like a scaled-down chamber orchestra, smaller than a full-sized orchestra in which each section of several musicians generally plays the same part, but larger than a string quartet, which often has four distinct voices playing at once.

Kim was the first violinist in the Elgar piece; his tone was exquisite throughout, never too loud or overbearing, and he blended well with Strauss and complemented Gregorian and Ms. Huang. Kim’s extended lead in the larghetto second movement was especially beautiful, as was Gregorian’s, later in the same section. The all-too-brief allegro movement that concluded the serenade was joyous but seemed to come to an almost premature closing.

The sextet embarked on the highly emotional Verklärte Nacht (“Transfigured Night”), Op. 4, by Arnold Schoenberg and really delivered the goods. One of Schoenberg’s earliest compositions and quite firmly in the late Romantic idiom, the piece depicts dark night with moonlight, conversation, emotional outbursts, calming response, and a fading away to darkness. Gregorian described the music, based on a poem by Richard Dehmel, as “Wagner on steroids,” combining “ecstasy and agony,” and that’s pretty much how it came across to the audience. One could hear an intense, emotionally charged piece constructed not unlike Richard Wagner’s Prelude und Liebestod, with perhaps some of the enigmatic phrase endings of Richard Strauss’ Also Sprach Zarathustra, even some of the harmonic austerity of Anton Bruckner.

The six musicians conveyed the various images, moods and feelings quite well, extending over about 30 minutes of uninterrupted playing. Some of the scoring let smaller ensembles within the sextet really shine: Ms. Huang as first violist and Kannen on cello in the first section, for instance; Gregorian later playing a lovely viola line over both cellos; and the two violins and two cellos forming a nice quartet. Kim’s first violin again provided wonderful tone and balance, as in a duet passage with cellist Kannen. The marked contrast between lush string and pizzicato playing occurred several times, and the long coda leading to the conclusion — perhaps the quietest moment in the entire piece — was such that the audience seemed to be holding its collective breath for the last note to fade away before exhaling.

An even more substantial piece closed the program and the season: Brahms’ String Sextet in B-flat, Op. 18. Strauss sat in the first violinist’s chair, Ms. Aznavoorian moved to first cello, and Gregorian returned to first violist’s chair. The program notes say this was Brahms’ first chamber work that did not include piano, and one could hear the type of scoring that sets his symphonies and serenades apart, based largely on his wonderful writing for lower strings.

Especially notable from a musical standpoint was the andante ma moderato second movement, a theme-and-variations faintly reminiscent of folk melodies, mostly minor-key until midway through, when a major-key variation breaks through. Each of the half-dozen variations begins with a different instrument or instruments, although the cellos do get considerable exposure. Some harmonies in the upper strings sounded almost like Celtic fiddles. The brief third movement, scherzo: allegro molto, was much lighter and quite dancelike, and the final rondo movement had several interesting sections, some weighted prominently on the lower strings. This movement, like parts of the Schoenberg piece, also had interesting contrasts between bowed and plucked strings. The movement moved deceptively toward a relaxed ending, but that was not to be. Gregorian and the others exchanged bowing and plucking, and he led a furious, intense, triple-time closing that was dazzling.